This invention relates to a cyclone dust collector capable of backwashing filters, which are provided in the interior of a cyclone body, independently of one another, and collecting and recovering dust (fine powder which is an object to be collected) efficiently. More particularly, the present invention relates to a cyclone dust collector structured compactly by uniting in one a cyclone body and a filter backwashing unit. Although the use of this cyclone dust collector is not specially limited, it is usefully provided in an already-installed glove box for the collection and recovery of dust of nuclear fuel substance therein carried out, for example, in a nuclear fuel pellet manufacturing step.
It is said that a cyclone dust collector and a bag filter-carrying dust collector are the main stream of apparatuses for collecting the dust included in a gas. However, these two kinds of dust collectors have advantages and disadvantages. The former is very simply constructed but low in dust collecting efficiency. The latter has a high dust collecting efficiency but it has a complicated construction and requires replacement of the filters, which have a short lifetime. Under the circumstances, a cyclone dust collector provided with a plurality of cylindrical filters in the interior of a dust collector body, in which a cyclone is utilized, has been developed as a dust collector for a nuclear fuel substance used in a nuclear fuel pellet manufacturing step.
An example of a conventional cyclone dust collector is shown in FIG. 5. The interior of a cyclone body 100 is divided into an upper space 106 and a lower space 108 by a partition member 104 which is provided with a plurality of cylindrical filters 102. A suction port 110 is provided so as to communicate with the lower space 108, and a common discharge port 112 is provided so as to communicate with the upper space 106. A collected dust recovery box 114 is fixed to the lower end of the cyclone body, and a discharge blower (not shown) is connected to the discharge port 112 of the cyclone body 100. Each of the cylindrical filters 102 is provided with a backwashing mechanism. Each backwashing mechanism is formed by fixing a backwashing nozzle 116 in a position in the upper space spaced from an upper portion of the corresponding cylindrical filter. A compressed air hose 120, having an electromagnetic switch valve 118, is connected to the backwashing nozzle 116.
When a dust-containing gas flows through the suction port into the cyclone body of such a cyclone dust collector, the gas flows downward as it rotates along the cylindrical inner wall surface thereof, and the dust flows toward the wall due to a centrifugal force exerted thereon, and is separated from the gas. In the meantime, the gas is discharged from the discharge port through the filters. Although fine dust continues to flow with the gas, it is separated and removed by the cylindrical filters when the gas flows therethrough.
In the filters, which have been used for a long period of time, clogging occurs due to the fine dust deposited thereon. This causes a pressure loss to increase, so that it becomes difficult to discharge the gas from the cyclone dust collector. In such a case, compressed air is ejected from the backwashing nozzles toward the filters, and a backwashing operation for shaking off the fine dust deposited on the filters is carried out.
In the cyclone dust collector of such a construction, a part of the compressed air ejected from the backwashing nozzles is discharged from the discharge port even during the backwashing operation. Therefore, the backwashing efficiency decreases, it is difficult to backwash the filters sufficiently, and it takes a long time to carry out backwashing operation. This causes the dust recovery efficiency to decrease.
The inventors of the present invention previously proposed (Japanese Patent Laid-open No. 8-309133/1996) a structure of a cyclone dust collector as a technique capable of solving these problems. The collector is formed by connecting the upper ends of cylindrical filters to their respective connecting pipes, one end of each of which is connected to a backwashing compressed air pipe via a three-way electromagnetic change-over valve, and the other end of each of which is connected to a pipe communicating with a gas discharging blower. In this dust collector, the backwashing of the filters and the discharging of the gas are switched from one to the other by the three-way electromagnetic change-over valves. Namely, the gas discharge system is closed and disconnected from the gas discharge blower, and, the supplying of backwashing compressed air is stopped during the discharging of the gas.
In such a structure, the lower end of each connecting pipe from which the backwashing air is ejected is Joined directly to the upper end of the corresponding filter, so that the backwashing efficiency becomes high, and a short-time sufficient filter backwashing operation is rendered possible. This enables the lifetime of the filters to be prolonged, and the dust recovery efficiency to be improved.
However, the construction of a header part including the dust collecting pipes and three-way electromagnetic change-over valves in an upper portion of the cyclone body becomes complicated and enlarged. In a newly installed facility, the space necessary for the installation of a cyclone dust collector can be secured in a glove box in a designing stage. However, in an existing glove box, a vacant space of only around 0.5 m.sup.3 is available, so that such a dust collector cannot be installed therein. When the facility is operated with no dust collector incorporated therein, the dust produced during the process scatters in the glove box, and workers have to carry out a manual cleaning operation by using brushes every time a process finishes, so that long period of time and many workers are required to carry out a cleaning operation. Therefore, there is a demand for developement of a dust collector having dimensions which are small enough so that the dust collector can be installed even in an existing glove box. The dust collector must also have aggregated dust collecting pipes, and have a simple construction so that the dust collector can be easily assembled.